1. Field of the Invention
The present invention relates to a pneumatic tire, more particularly to a heavy duty radial tire in which belt edge loosening can be effectively prevented.
2. Description of Related Art
Heavy duty radial tires for trucks, buses and the like having a relatively low aspect ratio are provided radially outside the carcass with a rigid belt which is generally composed of three or four plies of steel cords.
When the aspect ratio is less than 80% and the width of the belt exceeds the sectional height of the tire in particular, a strain at the belt edges caused when the tire rides over a curbstone and the like becomes relatively large, and at the edges of the radially innermost belt ply, a belt edge loosening failure is liable to occur. Thus, it is difficult to maintain the durability of such low aspect ratio tires.
In the laid-open Japanese Patent application JP-A-63-103705, a heavy duty radial tire is disclosed, wherein, in order to prevent the tread rubber from being separated from the edges of a four-ply belt, as shown in FIG. 3, a distance d2 of 1.5 to 4.5 mm is provided between the edges of the third belt ply b3 and the radially inner second belt ply b2. The exemplified tire is a 10.00R20-14PR tire, and the distance d1 between the edge of the inner belt ply b1 and the carcass (a) is depicted in a figure as being larger than (about twice) the distance d1.